CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDERS' EQUITY (UNAUDITED) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Additional Paid In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2011	$ 8,482,198	$ 1,216,234	$ 5,327,443	$ 2,032,556	$ (94,035)
Balance (in shares) at Dec. 31, 2011		486,494,000
Increase (Decrease) in Stockholders' Equity
Net income	366,953			366,953
Other comprehensive income (loss)	(7,971)				(7,971)
Dividends declared:
Common stock	(258,870)			(258,870)
Issuances of common stock	14,500	3,730	10,770
Issuances of common stock (in shares)		1,492,000
Repurchase of common stock	(18,529)	(1,750)	(16,779)
Repurchase of common stock (in shares)		(700,000)
Purchase of common stock for settlement of equity awards	(23,307)		(23,307)
Share-based compensation	18,531		18,531
Ending balance at Jun. 30, 2012	8,573,505	1,218,214	5,316,658	2,140,639	(102,006)
Balance (in shares) at Jun. 30, 2012		487,286,000
Beginning balance at Mar. 31, 2012	8,537,671	1,217,339	5,298,572	2,089,275	(67,515)
Balance (in shares) at Mar. 31, 2012		486,936,000
Increase (Decrease) in Stockholders' Equity
Net income	183,060			183,060
Other comprehensive income (loss)	(34,491)				(34,491)
Dividends declared:
Common stock	(131,696)			(131,696)
Issuances of common stock	9,357	875	8,482
Issuances of common stock (in shares)		350,000
Share-based compensation	9,604		9,604
Ending balance at Jun. 30, 2012	8,573,505	1,218,214	5,316,658	2,140,639	(102,006)
Balance (in shares) at Jun. 30, 2012		487,286,000
Beginning balance at Dec. 31, 2012	8,874,077	1,219,899	5,353,015	2,413,816	(112,653)
Balance (in shares) at Dec. 31, 2012	487,959,516	487,960,000
Increase (Decrease) in Stockholders' Equity
Net income	433,427			433,427
Other comprehensive income (loss)	818				818
Dividends declared:
Common stock	(274,308)			(274,308)
Issuances of common stock	243,125	23,340	219,785
Issuances of common stock (in shares)		9,336,000
Share-based compensation	23,106		23,106
Ending balance at Jun. 30, 2013	9,300,245	1,243,239	5,595,906	2,572,935	(111,835)
Balance (in shares) at Jun. 30, 2013	497,295,719	497,296,000
Beginning balance at Mar. 31, 2013	9,155,113	1,236,888	5,515,513	2,516,332	(113,620)
Balance (in shares) at Mar. 31, 2013		494,755,000
Increase (Decrease) in Stockholders' Equity
Net income	196,857			196,857
Other comprehensive income (loss)	1,785				1,785
Dividends declared:
Common stock	(140,254)			(140,254)
Issuances of common stock	74,291	6,351	67,940
Issuances of common stock (in shares)		2,541,000
Share-based compensation	12,453		12,453
Ending balance at Jun. 30, 2013	$ 9,300,245	$ 1,243,239	$ 5,595,906	$ 2,572,935	$ (111,835)
Balance (in shares) at Jun. 30, 2013	497,295,719	497,296,000